Vertebral implants adapted for posterior insertion

ABSTRACT

Disclosed is an endoprosthetic implant for a human spinal disc. The structure of the implant allows it to be inserted posteriorly. This insertion is accomplished by performing a partial discectomy in the affected region. An intervertebral space is then created by removing the fibrocartilage between the facing surfaces of adjacent vertebrae. The implant is then inserted into the intervertebral space. The implant is thus adapted to replace damaged or worn intervertebral discs. Furthermore, the structure of the implant, and its posterior insertion, alleviate most spinal pathologies.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of co-pending application Ser. No.10/696,727, filed Oct. 28, 2003 and entitled “Vertebral Implants AdaptedFor Posterior Insertion” (now U.S. Pat. No. 7,485,134); which is acontinuation-in-part of co-pending application Ser. No. 10/449,733,filed May 30, 2003 and entitled “Vertebral Implant with Dampening MatrixAdapted for Posterior Insertion” (now U.S. Pat. No. 7,052,515); which isa continuation-in-part of application Ser. No. 10/021,319, filed Dec. 7,2001 and entitled “Vertebral Implant Adapted for Posterior Insertion”(now U.S. Pat. No. 6,572,653). The contents of all prior applicationsare incorporated herein by reference in their entirety.

STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSOREDRESEARCH OR DEVELOPMENT

Not Applicable

REFERENCE TO A “SEQUENCE LISTING,” A TABLE, OR A COMPUTER PROGRAMLISTING APPENDIX SUBMITTED ON A COMPACT DISK

Not Applicable

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an endoprosthesis to replace an intervertebraldisc. More particularly, the present invention relates to anendoprosthetic implant that is specifically designed to be insertedposteriorly.

2. Description of the Background Art

The human spine is made up of twenty-four stacked segments calledvertebrae. Between adjacent vertebrae are small fibrocartilage cushionscalled intervertebral discs. These discs act as shock absorbers betweenadjacent vertebrae and permit the spinal column to bend. As bodilyforces are transmitted along spine, an individual disc can oftenencounter hundreds of pounds of force. Spinal forces are alsotransmitted by way of inferior and superior articular processes thatcontact each other at facet joints. Intervertebral discs and facetjoints are the two spinal mechanisms by which most spinal forces aretransmitted. Consequently, most spinal pathology occurs at theselocations.

For example, the fibrocartilage in the intervertebral discs oftenbecomes worn or damaged through wear, age and/or disease. This damagelimits spinal movements and can also result in pain as nerves becomepinched and swollen. Damaged fibrocartilage, in turn, increases thepressure that is otherwise encountered by the facet joint adjacent thedisc. This causes a premature wearing of the bone that makes up thejoint. Again, limited spinal movement and pain result.

One of the oldest methods of repairing damaged intervertebral discsinvolves fusing adjacent vertebrae by way of a bone graft. Such methods,however, have serious drawbacks in that the resulting fused vertebraelimit the overall movement of the spine. Furthermore, once two vertebraeare fused, the pressures encountered by adjacent healthy discs isincreased. This dramatically increases the likelihood that such healthydiscs may become damaged and worn. Thus, the fusing of vertebrae oftenpropagates the malady it seeks to cure.

Prosthetics are also employed to alleviate damaged intervertebral discs.This involves the removal of damaged fibrocartilage. The fibrocartilageis then replaced by an implant, typically formed from an elastomeric oran elastomeric composite. Prosthetic implants have the benefit ofproviding a more full range of spinal movement over fusion processes.Nonetheless, the elastomerics typically wear out over the life of theprosthetic. As a result, additional medical procedures are required toreplace the worn out prosthetic. Even prior to wearing out, elastomericsmay simply wear unevenly, whereby the prosthetic provides an unevenresilient force between the vertebrae. This causes nerves to becomepinched and swollen. Absent any type of wearing, elastomerics do notprovide a cushioning effect that is equivalent to naturally occurringfibrocartilage. Forces not absorbed by the elastomeric are thentransferred to the adjacent facet joint. This results in prematurewearing of the joint.

An example of a synthetic intervertebral disc is disclosed by U.S. Pat.No. 5,458,642 to Beer et al. Beer discloses the use of a syntheticintervertebral disc for implantation in the human body. The syntheticdisc includes a polymeric core that is inserted between two plates.Spring means are included in addition to the polymeric core. Each of theplates includes a tab that is secured to a vertebrae via a screw.

Additionally, U.S. Pat. No. 6,231,609 to Mehdizadeh discloses a discreplacement prosthesis. The prosthesis includes screw threads whichengage the vertebrae. A vertical stiffness is obtained from a series ofcoil springs affixed between upper and lower rigid members. The coilsprings also provide assistance in resisting shear forces.

U.S. Pat. No. 5,556,431 to Büttner-Janz discloses an intervertebral discendoprosthesis. The prosthesis includes two plates intermediate which aprosthesis core is included. The prosthesis core is made from apolyethylene. Bone screws are utilized in securing the two plates.

U.S. Pat. No. 5,824,093 to Ray discloses a prosthetic spinal discnucleus employing a hydrogel core surrounded by a constraining jacket.

Finally, U.S. Pat. No. 6,156,067 to Bryan et al. discloses a spinal discendoprosthesis with concave surfaces. A resilient body is includedintermediate the two surfaces.

Although each of the above-referenced inventions achieves its individualobjective, they all suffer from common problems. Namely, none of thebackground art discloses an endoprosthesis which is specificallydesigned to be inserted posteriorly to thereby eliminate the most commonsource of spinal pathology.

SUMMARY OF THE INVENTION

It is therefore one of the objectives of this invention to provide anintervertebral disc endoprosthesis which is specifically adapted to beinserted posteriorly.

It is also an object of this invention to provide an intervertebralendoprosthesis which utilizes a mechanical spring to achieve a longerwear life and accommodate increased intervertebral forces.

Still another object of this invention is to provide an endoprosthesiswhich substantially eliminates most posterior spinal pathology.

Yet another object of this invention is to provide an endoprosthesiswhich eliminates the need for facet joints.

These and other objectives are accomplished by providing a vertebralimplant adapted for posterior insertion and designed to replace thefibrocartilage between the facing surfaces of adjacent superior andinferior lumbar vertebrae. The implant includes two pairs ofhydroxyapatite-coated superior and inferior supports. Each supportincludes plate and lip portions. The lip portion is formed at a rightangle to the plate portion. In the case of the inferior support, the lipportion is offset to one side. The plate portion of each support furtherincludes a plurality of teeth, a retainer, and a pair of tapering sideedges. Each plate portion is received within a channel formed within oneof the facing surfaces of the superior or inferior vertebrae such thatthe lip portions abut the posterior edge of the vertebrae. In the caseof the inferior support, the offset lip accommodates a vertebralpedical.

The implant additionally includes a pair of springs. Each spring isformed from a plurality of oblong tapered coils. Each spring ispositioned between the side edges of opposing superior and inferiorsupports with the position of the spring being fixed by the opposingretainers. Each spring has an axial force under compression thatfunctions to drive the teeth of the opposing superior and inferiorsupports into the facing surfaces of the adjacent vertebrae.

The foregoing has outlined rather broadly the more pertinent andimportant features of the present invention in order that the detaileddescription of the invention that follows may be better understood sothat the present contribution to the art can be more fully appreciated.Additional features of the invention will be described hereinafter whichform the subject of the claims of the invention. It should beappreciated by those skilled in the art that the conception and thespecific embodiment disclosed may be readily utilized as a basis formodifying or designing other structures for carrying out the samepurposes of the present invention. It should also be realized by thoseskilled in the art that such equivalent constructions do not depart fromthe spirit and scope of the invention as set forth in the appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the nature and objects of the invention,reference should be had to the following detailed description taken inconnection with the accompanying drawings in which:

FIG. 1 is a posterior view of the lumbar region of a human spine;

FIG. 2 is a detailed illustration taken from FIG. 1;

FIG. 3 is a side elevational view of the implant of the presentinvention fully inserted and is taken from line 3-3 of FIG. 2;

FIG. 4 is a cross-sectional view taken from line 4-4 of FIG. 2;

FIG. 5 is a top plan view of the superior support;

FIG. 6 is a side elevational view of one of the superior supports;

FIG. 7 is a bottom plan view of one of the superior supports;

FIG. 8 is an end view taken along line 8-8 of FIG. 6;

FIG. 9 is an end view of one of the inferior supports;

FIG. 10 is an end view of one of the inferior supports;

FIG. 11 is a side elevational view of one of the springs;

FIG. 12 is a plan view of one of the springs;

FIG. 13 is an exploded view of the implant system of the presentinvention;

FIG. 14 is an alternative embodiment of the implant of the presentinvention; and

FIG. 15 is a view taken from line 15-15 of FIG. 14.

FIG. 16 is a detailed view taken from FIG. 1 of an alternative implantsystem of the present invention.

FIG. 17 is a side elevational view of alternative embodiment depicted inFIG. 16.

FIG. 18 is a top plan view taken along line 18-18 of FIG. 17.

FIG. 19 is a sectional view taken along line 19-19 of FIG. 18.

FIG. 20 is a sectional view of a lipless embodiment of the presentinvention.

FIG. 21 is a sectional view taken along line 21-21 of FIG. 20.

FIG. 22 is a posterior view of a screw shell embodiment of the presentinvention.

FIG. 23 is a sectional view taken along line 23-23 of FIG. 22.

FIG. 24 is a detailed view of one of the supports depicted in FIG. 22.

FIG. 25 is a view taken along line 25-25 of FIG. 24.

FIG. 26 is a view taken along line 26-26 of FIG. 24.

FIG. 27 is a detailed view of the offset lip of one of the inferiorsupports.

FIG. 28 is an end view of one of the screws employed in the screw shellembodiment.

FIG. 29 is a side elevational view of the screw of FIG. 28.

FIG. 30 is a detailed view of the screw shell depicted in FIG. 23.

FIG. 31 is an end view of the screw shell taken along line 31-31 of FIG.30.

FIG. 32 is an exploded view illustrating the screw prior to insertioninto the screw shell.

FIG. 33 is a posterior view of yet another alternative screw shellembodiment.

FIG. 34 is a sectional view taken along line 34-34 of FIG. 33.

FIG. 35 is posterior view of a rocker embodiment of the presentinvention.

FIG. 36 is a sectional view taken along line 36-36 of FIG. 35.

FIG. 37 is a detailed view of one of the superior bearing surfaces ofthe embodiment depicted in FIG. 35.

FIG. 38 is a side elevational view taken along line 38-38 of FIG. 37.

FIG. 39 is a detailed view of one of the inferior cups of the rockerembodiment depicted in FIG. 35.

FIG. 40 is a side elevational view of the cup taken along line 40-40 ofFIG. 39.

Similar reference characters refer to similar parts throughout theseveral views of the drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention relates to an endoprosthetic implant for a humanspinal disc. The structure of the implant allows it to be insertedposteriorly. This insertion is accomplished by performing a partialdiscectomy in the affected region. An intervertebral space is thencreated by removing the fibrocartilage between the facing surfaces ofadjacent vertebrae. The implant is then inserted into the intervertebralspace. The implant is thus adapted to replace damaged or wornintervertebral discs. Furthermore, the structure of the implant, and itsposterior insertion, alleviate most spinal pathologies. The implant ofthe present invention, and the manner in which it is employed, aredescribed in fuller detail hereinafter.

With reference now to FIG. 1, a posterior view of the lumbar region of ahuman spine is depicted. The implant of the present invention 20 isspecifically adapted for insertion between adjacent vertebrae in thislumbar region, specifically vertebrae L3 through S1. FIG. 1 illustratessome spinal anatomy, including: the spinous process 22; the superior andinferior articular processes (24 and 26, respectively); the transverseprocess 28; pedicals 32 and facet joints 34. FIG. 1 also illustrates adissected area with the spinous process 22 and superior and inferiorarticular processes (24 and 26) removed. This discectomy allows for theinsertion of the implant 20 of the present invention in a manner morefully described hereinafter.

FIG. 2 illustrates the implant 20 positioned between facing surfaces ofadjacent superior and inferior lumbar vertebrae (36 and 38,respectively). The implant 20 includes: an upper, or superior, pair ofsupports 44; a lower, or inferior, pair of supports 46; and two springs48. As illustrated, each spring 48 is positioned between alignedopposing superior and inferior supports (44 and 46). Thus, an individualsupport column 50 is defined by a superior and inferior support (44 and46) interconnected by a spring 48. The preferred form of the implantincludes two support columns 50. However, the use of other numbers ofcolumns, such as one or three, is within the scope of the presentinvention.

Each superior support 44 is defined by: first and second ends (52 and54); a cantilevered plate portion 56; and a lip portion 58. The plateportion 56 is cantilevered with the first end 52 being integral with thelip portion 58 and the second end 54 being free. This arrangement allowsthe plate 56 to pivot with respect to the sides of the support. Withreference now to FIG. 4, the relationship between the lip and plateportion (58 and 56) of a superior support 44 is depicted. Specifically,in the preferred embodiment, the lip portion 58 is formed at generally aright angle to the plate portion 56 at a first end 52 of the support 44.However, the exact angle between the lip portion 58 and the plateportion 56 varies due to the cantilevered nature of the plate. Withcontinuing reference to FIG. 4, the teeth 62 of the plate portion 56 aredepicted. These teeth 62 are formed by partially perforating the plate56 to create protrusions which rise above the planer surface of thesurrounding support 44. The teeth are preferably formed at a 90-degreeangle with the plate portion 56. The teeth 62 enable support 44 toengage the vertebral body in a manner more fully described hereinafter.Thus, although the teeth 62 have been described as perforations, theycould be formed in a variety of different ways. For example, the teeth62 could take the form of sharpened protuberances that are fixed to anouter surface of the plate 56, such as by welding. Additionally, theteeth 62 can be arranged in a number of different positions, other thanthe aligned orientation depicted. In the unbiased state of plate 56, thebottom of teeth 62 are flush with the bottom edge of the support 44(note FIG. 6). The plate 56 further includes a retainer 64 formed in amanner similar to the teeth 62. Again, the retainer 64 is formed byperforating the plate portion 56 to create a raised protrusion. Theretainer 64 functions in constraining the spring 48 positioned betweenthe facing supports (44 and 46). Thus, the teeth 62 are raised in adirection opposite to the direction in which the retainer 64 is raised.That is, the teeth 62 are raised in the same direction of the lip 58,and the retainer 64 is raised in the opposite direction.

FIGS. 5 through 7 are more detailed showings of the superior supports44. As can be appreciated from these figures, the superior supports 44further include raised side edges 66 which taper along the length of thesupport 44. That is, the side edges 66 are taller at the second end 54of the support and taper toward the first end 52 of the support untilthe edges are planar with the plate portion 56. The raised side edges66, along with the retainer 64, function in locking the spring 48 intoposition between opposing supports (44 and 46). Furthermore, due to thecantilevered nature of the plate 56, the side edges 66 are not connectedwith the edges of the plate 56.

With reference now to FIG. 4, the lower, or inferior supports 46, aredescribed. In most respects, the inferior supports 46 are identical tothe superior supports 44. That is, the inferior supports 46 are eachdefined by a first and second end (68 and 72), a cantilevered plateportion 74, and a lip portion 76. Again, the lip portion 76 is generallyformed at a right angle to the plate portion 74 at the first end 68 ofthe support 46. Furthermore, the plate portion 74 includes a pluralityof teeth 78 and a retainer 82, both of which are formed in the mannerdescribed in association with the superior support 44. Each of theinferior supports 46 similarly include raised side edges 84 which taperfrom the second end 72 to the first end 68 of the support 46.

With reference now to FIGS. 9 through 10, the primary difference betweenthe superior and inferior supports (44 and 46) will be described. Thatis, the lip 76 of the inferior support 46 is offset. More specifically,the lip portion 76 extends over only a portion of the width of thesupport 46. In the preferred embodiment depicted, the lip 76 extendsover approximately half of the width of the support 46. As such, the lipportion 76 is offset to one side. Furthermore, with the support 46positioned on the vertebrae, the adjacent lips 76 are preferablyoriented toward the medial portion of the vertebrae. This offset lipportion 76 is contrasted to the lips 58 of the superior supports 44which extend across the entire width of the support 44 (note FIG. 8).Thus, the lips 58 of the superior supports 44 are not offset.

The exact manner in which the supports (44 and 46) are positioned uponthe facing surfaces of the opposing vertebrae is next described inconjunction with the exploded view of FIG. 13. As illustrated, the twosuperior supports 44 are secured to the surface 86 of the superiorvertebrae 36, and the inferior supports 46 are secured to the facingsurface 88 of the inferior vertebrae 38. More specifically, the twosuperior supports 44 are received within channels 92 that are formedwithin the inferior surface 86 of the superior vertebrae 36. Thesechannels 92 are preferably formed after the medical practitioner hasconducted the partial discectomy. The channels 92 are ideallydimensioned to specifically receive the width of the supports 44 and arerelatively shallow when compared to the overall height of the support44. The channels 92 aid in orienting the supports 44 and limiting theirmovement once positioned. After the channels 92 are formed, the superiorsupports 44 are inserted over the surface 86 of the superior vertebrae36. This is done with the teeth 62 and lips 58 directed toward thevertebral body. However, at this stage the teeth 62 do not engage thevertebral body 36, insomuch as the plate 56 is unbiased and the teeth 62are flush with the lower surface of the support. As the supports 44 arepushed forward, the lip 58 of each support 44 will abut the posterioredge 94 of the vertebrae 36, which functions to properly orient thesupports 44 relative to the vertebral body 36. That is, each lip 58ensures that its corresponding support 44 does not extend too far ontothe vertebral body 36.

The above described insertion is repeated for the inferior supports 46.That is, the inferior supports 46 are inserted within channels 96 formedwithin the facing superior surface 88 of the inferior vertebrae 38.Again, with the supports 46 inserted, the teeth 78 do not engage thevertebral body 38. After the discectomy, the inferior vertebrae 38 willhave remaining pedicles 32 preventing insertion of a support with a fulllip. Thus, the lower supports 46 include the offset lip 76 thataccommodates the vertebral pedicle 32. Nonetheless, each offset lip 76still functions in limiting the insertion of its corresponding support46 into the corresponding channel 96.

The implant further includes springs 48 which are engaged between thefacing superior and inferior supports (44 and 46) as illustrated clearlyin FIG. 13. Each support column 50 includes one spring 48, with twosprings 48 being employed when two support columns 50 are used. Inpreferred embodiment, each of these springs 48 is a coil spring formedfrom a plurality of oblong coils. It has been found that the use of coilsprings increases the life of the implant over elastomeric springmembers. Preferably, each spring 48 is tapered from a second to a firstend. This spring geometry is illustrated in FIG. 11. Furthermore, FIG.12 is a plan view of the spring 48 showing its oblong or elongatedshape. The resulting free-standing orientation of the spring provides anarrower posterior profile 98 and a wider anterior profile 102. This, inturn, insures that the spring 48, when inserted, provides proper spinalcurvature.

With reference again to FIG. 13, the positioning of the springs 48between the supports (44 and 46) is described. Specifically, each spring48 is positioned such that the narrower end is adjacent the posterioredge of the spine and the wider end is adjacent the anterior edge of thespine. As indicated, this provides for proper spinal curvature with theimplant fully inserted. Each of the springs 48 is held in place byopposing superior and inferior supports (44 and 46), and further by theupstanding side walls of such supports (66 and 84) and their retainerportions (64 and 82). More specifically, the side walls prevent thelateral movement of the spring 48 and the retainer (64 or 82) precludesthe spring from moving longitudinally. When properly positioned, thesprings 48 are under compression and generate an axial force that servesto pivot the cantilevered plates 56 and 74 away from their correspondingsupports 44 and 46. As a consequence, the teeth 62 and 78 are forcedinto the vertebral bodies (36 and 38). This prevents any lateralmigration of the supports. When fully positioned, the springs absorb theforces between the superior and inferior vertebrae (36 and 38) and takethe place of the otherwise existing fibrocartilage.

Method of Insertion

The method by which the implant of the present invention is inserted isnext described. In the first step a partial discectomy is performed inorder to gain posterior access to the damaged area. This discectomyinvolves removing the spinous process 22 and inferior articular process26 from the superior vertebrae 36. The superior articular process 24 isalso removed from the inferior vertebrae 38. This exposes the thecalsac, which is moved to gain access to the fibrocartilage. Next, thedamaged fibrocartilage is removed to create an intervertebral space.This space provides access to the opposing vertebrae surfaces (86 and88). Once the space is created the upper and lower channels (92 and 96)can be formed. Specifically, two oblong channels 92 are formed withinthe surface 86 of the superior vertebrae 36, and two oblong channels 96are formed within the face 88 of the inferior vertebrae 38. Thesechannels (92 and 96) are formed in facing relation to one another.Thereafter, the two superior supports 44 are inserted into the channels92 with the lips 58 functioning to limit the insertion and otherwiseproperly orient the supports 44. The inferior supports 46 are thenlikewise positioned with the offset lips 76 engaging the remainingpedicles 32 on the inferior vertebrae 38. Lastly, the two springs 48 areinserted. More specifically, the first spring 48 is insertedintermediate the opposing superior and inferior supports (44 and 46) andthe second spring 48 is inserted between the remaining opposing superiorand inferior supports (44 and 46). In each instance, insertion of thespring causes the teeth to engage the vertebral body via action of thecantilevered plate.

FIGS. 14 and 15 illustrate yet another embodiment of the presentinvention. This embodiment is similar in most respects to the previouslydescribed embodiment. However, the two inferior supports 46 are eachprovided with a channel 104 formed along an interior edge. Thesechannels 104 are adapted to receive the sides of a spacer 106. That is,the opposing edges 108 of the spacer 106 are inserted within the facingchannels 104 of the inferior supports 46. This spacer 106 operates toabsorb any forces that would tend to operate individually on thesupports 46. Consequently, the spacer 106 functions in tying the twosupports 46 together such that they operate as an integral unit. Thespacer 106 is preferably positioned intermediate the channels 104 priorto insertion over the vertebral body.

All of the components of the above-described invention, that is thesuperior and inferior supports (44 and 46), and the springs 48 as wellas the spacer 106, are preferably formed from a titanium alloy or astainless steel. Furthermore, each of these components is preferablycoated with a hydroxyapatite to promote bone growth about the componentswhen in place.

Dampening Matrices (FIGS. 16-19)

An alternative embodiment of the present invention is depicted in FIGS.16-19. This alternative embodiment employs many of the same componentsdiscussed with reference to FIGS. 1 through 15, as such similarreference numerals are used to note similar components. However thisalternative embodiment further includes two dampening matrices 120. Eachmatrix 120 utilizes an identical construction and is positioned betweenthe superior and inferior supports (44 and 46) of the implant. Thedampening matrices each act as a cushion between the adjacent superiorand inferior lumbar vertebrae (36 and 38, respectively). Accordingly,when the opposing vertebrae are compressed the matrices slow the rate ofcompression and absorb the forces and loads encountered by the spinaltract. As noted below, this is achieved by the hydrogel core 122contained within each matrix.

Once the load is removed, resilient columns (or springs) provide areturn energy to reposition the adjacent vertebrae. This repositioningis achieved in the absence of loads upon the vertebral tract. In thepreferred embodiment, each of the resilient columns is positioned overand surrounds an associated dampening matrix. This arrangement isdepicted in FIG. 17.

In the preferred embodiment the dampening matrix is constructed from ahydrogel core positioned within a constraining jacket. This constructionis similar to the prosthetic spinal disc nucleus disclosed in U.S. Pat.No. 5,824,093 to Ray, the contents of which are incorporated herein byreference. As noted in Ray '093, the hydrogel core is formed as amixture of hydrogel polyacrylonitrile. In particular, acrylamide andacrylonitrile are used. Furthermore, the constraining jacket ispreferably a closed sack of a tightly woven high molecular weight hightenacity polymeric fabric. The jacket preferably contains openings thatare large enough to allow bodily fluids to react with the hydrogel core,but are small enough to prevent the hydrogel from escaping. Thus thehydrogel, which has an affinity for imbibing water, will deform andreform as necessary in order to accommodate and alleviate stresses andloads placed on the spinal tract. FIG. 19 is a cross-sectional viewillustrating the hydrogel core of the present invention.

After any loads applied to the hydrogel core are removed the resilientcolumns then return the opposing vertebrae to their proper orientation.In this regard, the preferred resilient column has been disclosed as aspring 48. However any other resilient tensioning devices known in theart can be employed. For example, the column can be formed from a leafspring, coil spring, resilient coiled polymer or a continuous polymersleeve.

Lipless Embodiment (FIGS. 20-21)

The embodiment depicted in FIGS. 20-21 is the same in most respects tothe implant described in conjunction with FIGS. 2 through 13. Thenotable difference, however, is that the superior and inferior supports(132 and 134) have no lip portions hanging over the posterior end of theupper and lower vertebral bodies. Consequently, as illustrated in FIG.21, the first ends 136 of the superior and inferior supports (132 and134) terminate adjacent the respective vertebral bodies. This “lipless”embodiment is advantageous because when the implants are fully insertedthe supports are unexposed. This embodiment also weighs less than theembodiment of FIGS. 2-13.

Nonetheless, in this lipless embodiment there are no portions of thesupports that overhang to prevent the supports from extending too fartowards the anterior end of the vertebral bodies. That is, there are nolips to prevent the over insertion of the support. Rather, the correctorientation between an individual support and its correspondingvertebral surface is achieved via channels 138 formed within thevertebral surfaces and teeth 142 formed within each support. Thesefeatures ensure a positive fit between vertebrae and prevent overinsertion.

In all other respects, the lipless embodiment is the same as theembodiment depicted in FIGS. 2-13. That is, both the superior andinferior supports (132 and 134) include a cantilevered lower surface 144into which a retainer 146 and a series of teeth 142 are formed. Eachsupport further includes tapering side edges 148. Insertion is achievedby performing a discectomy to create an intervertebral space as noted inconjunction with the primary embodiment. Thereafter, upper and lowerchannels 138 are formed in the surfaces of the vertebral body, with thesupports being positioned within these channels. Thereafter, springs 152are inserted bilaterally between the pair of superior and inferiorsupports (132 and 134). Again, as noted in conjunction with the primaryembodiment, each retainer 146 functions in preventing the movement ofthe spring 152.

Screw Shell Embodiment (FIGS. 22-34).

The next embodiment is described in conjunction with FIGS. 22-34. Aswith the primary embodiment, this embodiment includes two superiorsupports and two inferior supports (154 and 156, respectively) that arepositioned bilaterally in an intervertebral space. In this embodiment,two rounded inserts are secured between the supports. These inserts areinterconnected by way of a screw. Thus, each pair of inserts takes on a“screw shell” configuration.

The intervertebral space is again created in the manner described inconjunction with the primary embodiment. Namely, a discectomy isperformed and two superior channels and two inferior channels are formedin the opposing faces of the intervertebral space. After the space iscreated, the superior and inferior supports (154 and 156) are insertedinto these channels. As with the supports in the primary embodiment, thesupports in the screw shell embodiment preferably include lips to limittheir insertion into the intervertebral space. Specifically, thesuperior supports 154 include full-width lips 158 that are dimensionedto engage the entire corresponding edge of the superior vertebrae. Theinferior supports 156 likewise include offset lips 162 as depicted inFIG. 22. These lips 162 encompass only a portion of the support width.In the preferred embodiment, the lips 162 extend over approximatelyone-half of the width of the support and are oriented towards the medialportion of the vertebrae. With this configuration, the inferior lips 162accommodate the pedicles (which may be partially dissected) extendingfrom the posterior face of the vertebrae. Furthermore, as noted in FIG.23, both the superior and inferior supports (154 and 156) can furtherinclude interior lips located at the second ends of each support thatprevent over insertion of the screw shell.

The supports of this embodiment differ from the primary embodiment inthat they each include a trough 164 formed along their lengths. Thistrough, which is illustrated in FIG. 24, takes the form of an arcuatesegment, which is removed from the body of the support. Additionally,unlike the primary embodiment, the supports of the screw-shellembodiment have neither a cantilevered floor or teeth. These arcuateportions of the supports permit proper placement of the screw shellinserts. That is, with the supports properly positioned in facingrelation, adjacent upper and lower troughs 164 form opposing arcuatesurfaces that are dimensioned to accommodate the upper and lower inserts(166 and 168, respectively) (note FIG. 23). The arcuate upper and lowerinserts (166 and 168), in turn, form a single shell 172. Two such shells172 are bilaterally positioned within the intervertebral space (noteFIG. 22).

The upper and lower inserts (166 and 168) are preferably interconnectedby way of a screw 174. The interconnection is achieved by threading theinternal surfaces of the inserts in a manner that permits a screw to bethreadably positioned between the upper and lower inserts. Thisconfiguration allows for the lateral movement of the screw 174 betweeneither end of the screw shell 172 upon screw rotation. To enable thescrew 174 to be threaded into and out of the screw shell 172, eachincludes a hexagonal opening 176 at its end to facilitate physicianrotation of the screw via a matching key.

With continuing reference to FIG. 23, the arcuate upper and lowerportions of the screw shell are depicted. This cross-sectional viewillustrates the threaded internal surfaces of the inserts (166 and 168)and how they cooperate with a screw 174. The cross-section furtherillustrates how the arcuate portions of the inserts conform to thetroughs 164 of the superior and inferior supports (154 and 156). In thepreferred embodiment, the inserts are not permanently affixed to thecorresponding support, but rather simply rest within the correspondingtrough.

With reference now to FIG. 30, it can be seen that the anterior end 178of each insert is enlarged with respect to the posterior end.Accordingly, when the inserts (166 and 168) are positioned between thesupports (154 and 156) prior to screw insertion, the enlarged anteriorportions promote a lordosis of the spine. This configuration alsoprovides for an enlarged posterior opening of the resulting screw shelland a narrowed anterior opening. This “steady state” configuration canbe subsequently overcome by inserting a screw into the threaded interiorof the screw shell. Specifically, by driving a screw 174 from theposterior to the anterior region of the screw shell 172 the narrowedanterior opening of the screw shell is widened to thereby correct thelordosis (note FIG. 23). Proper spinal curvature is promoted by fullinsertion of the screw shell. Full screw insertion represents the finalsurgical step.

In an alternative embodiment of the screw shell, the lips of thesuperior and inferior supports (154 and 156) are removed. In thisembodiment, depicted in FIGS. 33-34, when the supports are inserted inthe intervertebral space, their posterior edges are flush with theadjacent vertebral bodies. Yet in another alternative construction, thescrew positioned between adjacent inserts is replaced by a helicalspring 182. This is similar to the prior embodiment, however, the springhas the advantage of both interconnecting the facing inserts andproviding resistance. As with the prior embodiment, each support wouldhave an interior surface that accommodates the periphery of the spring182.

Rocker Embodiment (FIGS. 35-40)

The final embodiment is depicted in conjunction with FIGS. 35-40. Thisembodiment again includes superior and inferior supports 186, which arepositioned within the opposing surfaces in the intervertebral space.However, in this embodiment, the supports 186 are fitted into channels184 that are both deepened and made more narrow. These channels 184accommodate a rail 188 running along the lower surface of each support186. It has been found that this rail 188 promotes a stableinterconnection between the support and vertebral surface. Also, as isknown in the art, the supports may include a hydroxyappetite coating tofacilitate bone growth.

Upon each of the superior supports, an arcuate bearing surface 192 issecured. This interconnection can be achieved via a suitable adhesive ormechanical fastener. This bearing surface 192 is preferably formed froma suitable metallic or polyethylene material. Concave receptacles 194,which are also formed from a metallic or polyethylene material, aresimilarly secured to the inferior supports. The receptacles 194 aredimensioned to accommodate each of the superior bearing surfaces 192. Inthis manner, once these supports are secured, the interaction betweenthe bearing surfaces and the cups allows for a limited posterior andanterior range of motion, while at the same time limiting lateralmotion.

The present disclosure includes that contained in the appended claims,as well as that of the foregoing description. Although this inventionhas been described in its preferred form with a certain degree ofparticularity, it is understood that the present disclosure of thepreferred form has been made only by way of example and that numerouschanges in the details of construction and the combination andarrangement of parts may be resorted to without departing from thespirit and scope of the invention.

1. A vertebral implant for insertion between adjacent vertebrae havinganterior and posterior faces comprising: a superior support positionedupon a vertebral surface, the superior support having a posterior edgewhich is flush with a posterior vertebral face, the superior supporthaving an arcuate trough formed therein; an inferior support positionedupon a vertebral surface in facing relation to the superior support suchthat a posterior edge of the inferior support is flush with a posteriorvertebral face, the interior support having an arcuate trough formedtherein; a two part shell positioned intermediate the superior andinferior supports, the two part shell having arcuate upper and lowersurfaces that correspond to the arcuate troughs formed within thesuperior and inferior supports; a threaded screw positioned within thetwo part shell, rotation of the screw causing its lateral movement tothereby adjust the spacing between the two parts of the shell.
 2. Avertebral implant for insertion into an intervertebral space havinganterior and posterior areas comprising: superior and inferior supportspositioned upon a vertebral surface in facing relation to one another,both supports being positioned in the posterior area of theintervertebral space; an insert positioned intermediate the superior andinferior supports, the insert adapted to absorb forces generated in theintervertebral space.
 3. The implant as described in claim 2 wherein theinsert is formed from upper and lower portions.
 4. The implant asdescribed in claim 3 wherein the upper and lower portions areinterconnected via a threaded element, wherein movement of the threadedelement causes relative movement of the upper and lower portions.
 5. Theimplant as described in claim 2 wherein the superior and inferiorsupports each include lips that are adapted to hang over an edge of thevertebral body.
 6. A vertebral implant specifically adapted forposterior insertion comprising: a superior support positioned upon avertebral surface, the superior support having a posterior edge which isflush with a posterior vertebral face; an inferior support positionedupon a vertebral surface in facing relation to the superior support suchthat a posterior edge of the inferior support is flush with a posteriorvertebral face; a member positioned intermediate the superior andinferior supports.
 7. The vertebral implant as described in claim 6wherein the member is in the form of a shell with arcuate upper andlower portions.
 8. The vertebral implant as described in claim 6 whereinthe member is a dampening matrix.
 9. The vertebral implant as describedin claim 6 wherein the superior and inferior supports include anoverhanging lip portion.
 10. The vertebral implant as described in claim6 wherein a spring is positioned between the superior and inferiorsupports.
 11. A surgical method for replacing damaged fibrocartilagebetween facing superior and inferior vertebrae in the lumbar region of apatient's spine, the patient having a posterior region, the superiorvertebrae including an outer surface, a spinous process and an inferiorarticular process, the inferior vertebrae including an outer surface, asuperior articlular process and pedicals, the method being carried outin a manner that reduces most posterior spinal pathology, the methodcomprising the following steps: accessing the facing superior andinferior vertebrae through the posterior region of the patient;performing a partial discectomy in order to gain access to the damagedfibrocartilage, the discectomy including removing the spinous processand the inferior articular process of the superior vertebrae and thesuperior articular process of the inferior vertebrae; removing thedamaged fibrocartilage to create an intervertebral space, theintervertebral space providing access to opposing vertebral surfaces ofthe superior and inferior vertebrae; forming superior and inferiorchannels within the opposing vertebral surfaces, the superior andinferior channels being in facing relation to one another; providingsuperior and inferior supports, each of the supports including a plateportion and a lip, with the lip of the inferior support being offset;inserting the supports within the channels such that the lips of thesupports contact the outer vertebral surfaces to thereby limit theinsertion of the supports, the offset lip of the inferior supportaccommodating the pedical of the inferior vertebrae; inserting acushioning member in between the superior and inferior supports, thecushioning member functioning to replace the fibrocartilage and absorbforces applied to the intervertebral space.
 12. The method as describedin claim 11 wherein the cushioning member is a coil spring.
 13. Themethod as described in claim 11 wherein the cushioning member is adampening matrix comprising a hydrogel core positioned within aconstraining jacket.
 14. The method as described in claim 11 wherein thecushioning member includes two rounded inserts that are interconnectedby a screw.
 15. A surgical method for replacing damaged fibrocartilagebetween facing superior and inferior vertebrae, the method being carriedout in a manner that reduces most posterior spinal pathology, theinferior vertebrae through a posterior region of a patient; removing thedamaged fibrocartilage to create an intervertebral space; providingsuperior and inferior supports, each of the supports including a plateportion; inserting the superior and inferior supports into theintervertebral space; positioning a cushioning member in between thesuperior and inferior supports, the cushioning member functioning toreplace the fibrocartilage and absorb forces applied to theintervertebral space.
 16. The method as described in claim 15 whereinaccess to the damaged fibrocartilage is gain by performing a partialdiscectomy.
 17. The method as described in claim 15 wherein channels areformed within the intervertebral space prior to inserting the supports.18. The method as described in claim 15 wherein the superior andinferior supports include lip portions that limit the insertion of thesupports into the intervertebral space.
 19. The method as described inclaim 18 wherein the lip portion of the inferior support is offset. 20.A surfical method for repairing a vertebral disc comprising: posteiorlyaccessing the damaged vertebral disc; posteriorly removing the damagedvertebral disc to create an intervertebral space; providing opposingsupports and positioning the supports into the intervertebral space;positioning a cushioning member in between the opposing supports, thecushioning member functioning to replace the damaged disc.